PROJECT SUMMARY/ABSTRACT In Uganda, only one-fifth of HIV-positive adults are aware of their serostatus, far short of the UNAIDS 90% target for ending the epidemic. Perceived social norms, defined as one?s perceptions about which attitudes and behaviors are held and engaged in by majority of a social group, are understudied as potential drivers of HIV testing. The preliminary data from my dissertation fieldwork in rural Uganda showed that most people thought that most people in their village had never been tested for HIV even though most had actually been tested, and that men who (mistakenly) perceived HIV testing as uncommon were 3 times more likely to have never been tested themselves. My long-term career goal is to become an independent investigator with mixed-methods expertise in understanding how perceived social norms drive HIV testing, and to develop, test, and implement strategies to improve HIV testing. Although I have completed my PhD in social epidemiology, to achieve research independence I need additional mentorship and training in [1] qualitative research methods, [2] advanced statistical methods such as multilevel and longitudinal modeling, and [3] HIV-related intervention development in sub-Saharan Africa. The proposed training will enable me to achieve my scientific objective: to test the extent to which perceived social norms can affect one?s propensity to engage in HIV testing, and to develop a pilot intervention to increase testing in Uganda among men, women, and couples. My central hypothesis, based on my dissertation fieldwork, is that people misperceive HIV testing as uncommon within salient reference groups, and that these misperceptions greatly undermine their own propensity to undergo HIV testing. I further hypothesize that correcting these misperceptions will be a feasible and acceptable way to increase testing. I will test my central hypothesis by pursuing 3 specific aims: (1) Use qualitative research methods to design valid questions that elicit perceived social norms about HIV testing within different reference groups, including men-only, women-only, and couples-only subgroups of different backgrounds and experiences; (2) Estimate the extent to which social norms for HIV testing are misperceived and perceptions are associated with personal testing; and (3) Develop and test the feasibility, acceptability, and preliminary effectiveness of a pilot intervention to increase HIV testing among men, women, and couples. I am well- positioned to accomplish these aims given my strong preliminary data directly related to the content of the proposed K01 award and my mentors' combined expertise. My approach is innovative in its use of mixed methods to test theoretically-driven hypotheses about the extent to which perceived social norms about HIV testing within salient reference groups affect HIV testing behavior. The proposed research will have significant public health impact because it will lead to the development of a unique class of interventions to increase HIV testing in resource-limited settings, a necessity for ending the HIV epidemic in sub-Saharan Africa.